In the 3rd Generation Partnership Project (3GPP), which is a mobile communication system standardization project, the formulation of specifications of a Device to Device Proximity Service (D2D ProSe) is promoted.
Here, as one of functions of the D2D ProSe, there is a function (ProSe UE-to-Network Relaying) of relaying data between a radio terminal (remote user equipment (UE)) located outside the coverage of a cell and a network, using the D2D ProSe, by another radio terminal (ProSe UE-to-Network Relay).